Generally, in the video apparatus such as a color television or a video camera, since the spot of the electron beam in cathode ray tube or camera tube has a limited size, a so-called aperture distortion can be generated, so that the horizontal or vertical resolution is lowered in the high frequency region of the picture.
An example of the conventional aperture compensating circuit to eliminate such an aperture distortion is illustrated in FIG. 1.
The aperture compensating circuit as illustrated in FIG. 1 comprises a differential amplifying circuit having transistors Q1, Q2, bias resistors R1 to R5, a delay line DL provided between collectors of said transistors Q1 and Q2, and a variable resistor VR1 connected to the emitter of the said transistors Q1 and Q2 to preset the aperture edge quantity.
However, in the conventional circuit comprised as above, the aperture edge quantity is large in case that the level difference of the adjacent luminance signals is large, and is small in case that the level difference of luminance signals is small. Therefore, even if the average value of luminance signal level is high, when the level difference is small, only the small edge quantity is added to the luminance signal.
As a result, the desirable compensating effect can not be attained and S/N ratio is lowered, thereby deteriorating the image quality.